Inert-dominant pulsing in plasma processing systems

ABSTRACT

A method for processing substrate in a processing chamber, which has at least one plasma generating source and a gas source for providing process gas into the chamber, is provided. The method includes exciting the plasma generating source with an RF signal having RF frequency. The method further includes pulsing the gas source, using at least a first gas pulsing frequency, such that a first process gas is flowed into the chamber during a first portion of a gas pulsing period and a second process gas is flowed into the chamber during a second portion of the gas pulsing period, which is associated with the first gas pulsing frequency. The second process gas has a lower reactant-gas-to-inert-gas ratio relative to a reactant-gas-to-inert-gas ratio of the first process gas. The second process gas is formed by removing at least a portion of a reactant gas flow from the first process gas.

PRIORITY CLAIM

This application claims priority under 35 USC. 119(e) to acommonly-owned provisional patent application entitled “INTER-DOMINANTPULSING IN PLASMA PROCESSING SYSTEMS”, U.S. Application No. 61/560,005,filed on Nov. 15, 2011 by Keren Jacobs Kanarik all of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

Plasma processing systems have long been employed to process substrates(e.g., wafers or flat panels or LCD panels) to form integrated circuitsor other electronic products. Popular plasma processing systems mayinclude capacitively coupled plasma processing systems (CCP) orinductively coupled plasma processing systems (ICP), among others.

Generally speaking, plasma substrate processing involves a balance ofions and radicals (also referred to as neutrals). For example, with aplasma that has more radicals than ions, etching tends to be morechemical and isotropic. With a plasma that has more ions than radicals,etching tends to be more physical and selectivity tends to suffer. In atraditional plasma chamber, ions and radicals tend to be closelycoupled. Accordingly, the process window (with respect to processingparameters) tends to be fairly narrow due to the fact that there arelimited control knobs to independently achieve an ion-dominant plasma ora radical-dominant plasma.

As electronic devices become smaller and/or more complex, etchingrequirements such as selectivity, uniformity, high aspect ratio, aspectdependent etching, etc., have increased. While it has been possible toperform etches on the current generation of products by changing certainparameters such as pressure, RF bias, power, etc., the next generationof smaller and/or more sophisticated products demand different etchcapabilities. The fact that ions and radicals cannot be more effectivelydecoupled and independently controlled has limited and in some casesmade it impractical to perform some etch processes to manufacture thesesmaller and/or more sophisticated electronic devices in some plasmaprocessing systems.

In the prior art, attempts have been made to obtain plasma conditions tomodulate the ion-to-radical ratio at different times during an etch. Ina conventional scheme, the source RF signal may be pulsed (e.g., on andoff) in order to obtain a plasma that has the normal ion to neutral fluxratio during one phase of the pulse cycle (e.g., the pulse on phase) anda plasma with lower ion to neutral flux ratio during another phase ofthe pulse cycle (e.g., during the pulse off phase). It is known thatsource RF signal may be pulsed synchronously with bias RF signal.

However, it has been observed that while the prior art pulsing has, tosome extent, resulted in alternate phases of normal ion to neutral fluxratio plasmas at different points in time and has opened up theoperating window for some processes, larger operating windows are stilldesired.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 shows, in accordance with one or more embodiments of theinvention, an example combination pulsing scheme where the input gas(such as reactant gas and/or inert gas) and the source RF signal areboth pulsed, albeit at different pulsing frequencies.

FIG. 2 shows, in accordance with one or more embodiments of theinvention, another example combination pulsing scheme.

FIG. 3 shows, in accordance with one or more embodiments of theinvention, yet another example combination pulsing scheme.

FIG. 4 shows, in accordance with one or more embodiments of theinvention, other possible combinations for the combination pulsingscheme.

FIG. 5 shows, in accordance with one or more embodiments of theinvention, the steps for performing combination pulsing.

FIG. 6 shows, in accordance with one or more embodiments of theinvention, the steps for performing gas pulsing.

FIGS. 7A and 7B illustrate, in accordance with embodiments of theinvention, different example variations of the gas pulsing schemediscussed in connection with FIG. 6.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will now be described in detail with reference toa few embodiments thereof as illustrated in the accompanying drawings.In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art, that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process steps and/or structureshave not been described in detail in order to not unnecessarily obscurethe present invention.

Various embodiments are described hereinbelow, including methods andtechniques. It should be kept in mind that the invention might alsocover articles of manufacture that includes a computer readable mediumon which computer-readable instructions for carrying out embodiments ofthe inventive technique are stored. The computer readable medium mayinclude, for example, semiconductor, magnetic, opto-magnetic, optical,or other forms of computer readable medium for storing computer readablecode. Further, the invention may also cover apparatuses for practicingembodiments of the invention. Such apparatus may include circuits,dedicated and/or programmable, to carry out tasks pertaining toembodiments of the invention. Examples of such apparatus include ageneral-purpose computer and/or a dedicated computing device whenappropriately programmed and may include a combination of acomputer/computing device and dedicated/programmable circuits adaptedfor the various tasks pertaining to embodiments of the invention.

Embodiments of the invention related to a combination pulsing schemethat pulses the input gas (e.g., reactant gases and/or inert gases)using a first pulsing frequency and the source RF signal at a differentsecond pulsing frequency. Although an inductively coupled plasmaprocessing system and an inductive RF power source are employed todiscuss in the examples herein, it should be understood that embodimentsof the invention apply equally to capacitively coupled plasma processingsystems and capacitive RF power sources.

In one or more embodiments, the input gas is pulsed at a slower pulsingfrequency, and the inductive source RF signal is pulsed at a different,faster pulsing frequency in an inductively coupled plasma processingsystem. For example, if the inductive source RF signal is at 13.56 MHz,the inductive source RF signal may be pulsed at, for example, 100 Hzwhile the gas is pulsed at a different pulsing rate, such as 1 Hz.

Thus, a complete gas pulse cycle is 1 second in this example. If the gaspulsing duty cycle is 70%, the gas may be on for 70% of the 1-second gaspulsing period and off for 30% of the 1-second gas pulsing period. Sincethe source RF pulsing rate is 100 Hz, a complete RF signal pulsingperiod is 10 ms. If the RF pulsing duty cycle is 40%, the RF on-phase(when the 13.56 MHz signal is on) is 40% of the 10 ms RF pulsing periodand the RF off phase (when the 13.56 MHz signal is off) is 60% of the 10ms RF pulsing period.

In one or more embodiments, the inductive source RF signal may be pulsedwith two different frequencies while the gas is pulsed at its own gaspulsing frequency. For example, the aforementioned 13.56 MHz RF signalmay be pulsed not only at frequency f1 of 100 Hz but may also be pulsedwith a different, higher frequency during the on-phase of frequency f1.For example, if the RF pulsing duty cycle is 40% of the f1 pulse, theon-phase of f1 is 40% of 10 ms or 4 ms. However, during that 4 mson-phase of f1, the RF signal may also be pulsed at a different, higherfrequency of f2 (such as at 400 Hz).

Embodiments of the invention contemplate that the gas pulses and RFpulses may be synchronous (i.e., with matching leading edge and/orlowering edge of the pulse signals) or may be asynchronous. The dutycycle may be constant or may vary in a manner that is independent of theother pulsing frequency or in a manner that is dependent on the otherpulsing frequency.

In one or more embodiments, frequency chirping may be employed. Forexample, the RF signal may change its fundamental frequency in aperiodic or non-periodic manner so that during a phase or a portion of aphase of any of the pulsing periods (e.g., any of the RF signal or gaspulsing periods), a different frequency (e.g., 60 MHz versus 13.56 MHz)may be employed. Likewise, the gas pulsing frequency may be changed withtime in a periodic or non-periodic manner if desired.

In one or more embodiments, the aforementioned gas and source RF pulsingmay be combined with one or more pulsing or variation of anotherparameter (such as pulsing of the bias RF signal, pulsing of the DC biasto the electrode, pulsing of the multiple RF frequencies at differentpulsing frequencies, changing the phase of any of the parameters, etc.)

The features and advantages of embodiments of the invention may bebetter understood with reference to the figures and discussions thatfollow.

FIG. 1 shows, in accordance with an embodiment of the invention, anexample combination pulsing scheme where the input gas (such as reactantgas and/or inert gas) and the source RF signal are both pulsed, albeitat different pulsing frequencies. In the example of FIG. 1, the inputgas 102 is pulsed at a gas pulsing rate (defined as 1/T_(gp), whereT_(gp) is the period of the gas pulse) of about 2 seconds/pulse or 2MHz.

The TCP source RF signal 104 of 13.56 MHz is pulsed at a RF pulsing rate(defined as 1/T_(rfp), where T_(rfp) is the period of the RF pulsing).To clarify the concept of RF pulsing herein, the RF signal is on (suchas the 13.56 MHz RF signal) during the time period 120 and the RF signalis off during the time period 122. Each of the gas pulsing rate and theRF pulsing rate may have its own duty cycle (defined as the pulseon-time divided by the total pulsing period). There are no requirementsthat the duty cycle has to be 50% for any of the pulse signals, and theduty cycle may vary as needed for a particular process.

In an embodiment, the gas pulsing and the RF signal pulsing are at thesame duty cycle. In another embodiment, the gas pulsing and the RFsignal pulsing are at independently controllable (and may be different)duty cycles to maximize granular control. In one or more embodiments,the leading and/or trailing edges of the gas pulsing signal and the RFpulsing signal may be synchronous. In one or more embodiments, theleading and/or trailing edges of the gas pulsing signal and the RFpulsing signal may be asynchronous.

In FIG. 2, the gas input 202 is pulsed at its own gas pulsing frequency.However, the source RF signal 204 may be pulsed with two differentfrequencies while the gas is pulsed at its own gas pulsing frequency(defined as 1/T_(gp), where T_(gp) is the period of the gas pulse). Forexample, the RF signal may be pulsed not only at frequency f1 (definedas 1/T_(f1) from the figure) but may also be pulsed with a different,higher frequency during the on-phase of f1 pulsing. For example, duringthis on-phase of f1 pulsing, the RF signal may be pulsed at a differentpulsing frequency f2 (defined as 1/T_(f2) from the figure).

In FIG. 3, the gas input 302 is pulsed at its own gas pulsing frequency.However, the source RF signal 304 may be pulsed with three differentfrequencies while the gas is pulsed at its own gas pulsing frequency.For example, the RF signal may be pulsed not only at frequency f1(defined as 1/T_(f1) from the figure) but may also be pulsed with adifferent, higher frequency during the on-phase of f1 pulsing. Thus,during this on-phase of f1 pulsing, the RF signal may be pulsed at adifferent pulsing frequency f2 (defined as 1/T_(f2) from the figure.During the off-phase of f1 pulsing, the RF signal may be pulsed at adifferent pulsing frequency f3 (defined as 1/T_(f3) from the figure).

Additionally or alternatively, although the duty cycle is shown to beconstant in the examples of FIGS. 1-3, the duty cycle may also vary, ina periodic or non-periodic manner and independently or dependently onthe phases of one of the pulsing signals (whether gas pulsing signal, RFpulsing signal, or otherwise). Further, the change in the duty cycle maybe synchronous or asynchronous with respect to phase of any one of thepulsing signals (whether gas pulsing signal, RF pulsing signal, orotherwise).

In one embodiment, the duty cycle of the RF pulsing is advantageouslyset to be one value during the on-phase of the gas pulse (e.g., 154 inFIG. 1), and the duty cycle of the RF pulsing is set to be anotherdifferent value during the off-phase of the gas pulse (e.g., 156 of FIG.1). In a preferred embodiment, the duty cycle of the RF pulsing isadvantageously set to be one value during the on-phase of the gas pulse(e.g., 154 in FIG. 1) and the duty cycle of the RF pulsing is set to bea lower value during the off-phase of the gas pulse (e.g., 156 of FIG.1). It is contemplated that this RF pulsing duty cycle embodimentwherein the duty cycle is higher during the on phase of the gas pulsingand lower during the off phase of the gas pulsing is advantageous forsome etches. It is contemplated that this RF pulsing duty cycle variancewherein the duty cycle is lower during the on phase of the gas pulsingand higher during the off phase of the gas pulsing is advantageous forsome etches. As the term is employed herein, when a signal is pulsed,the duty cycle is other than 100% during the time when the signal ispulsed (i.e., pulsing and “always on” are two different concepts).

Additionally or alternatively, frequency chirping may be employed withany of the pulsing signals (whether gas pulsing signal, RF pulsingsignal, or otherwise). Frequency chirping is described in greater detailin connection with the RF pulsing signal in FIG. 4 below.

In one or more embodiments, the gas is pulsed such that during the gaspulsing on phase, reactant gas(es) and inert gas(es) (such as Argon,Helium, Xenon, Krypton, Neon, etc.) are as specified by the recipe.During the gas pulsing off phase, at least some of both the reactantgas(es) and inert gas(es) may be removed. In other embodiments, at leastsome of the reactant gas(es) is removed and replaced by inert gas(es)during the gas pulsing off phase. In an advantageous, at least some ofthe reactant gas(es) is removed and replaced by inert gas(es) during thegas pulsing off phase to keep the chamber pressure substantially thesame.

In one or more embodiments, during the gas pulsing off phase, thepercentage of inert gas(es) to total gas(es) flowed into the chamber mayvary from about X% to about 100%, wherein X is the percentage of inertgas(es) to total gas flow that is employed during the gas pulsing onphase. In a more preferred embodiment, the percentage of inert gas(es)to total gas(es) flowed into the chamber may vary from about 1.1 X toabout 100%, wherein X is the percentage of inert gas(es) to total gasflow that is employed during the gas pulsing on phase. In a preferredembodiment, the percentage of inert gas(es) to total gas(es) flowed intothe chamber may vary from about 1.5 X to about 100%, wherein X is thepercentage of inert gas(es) to total gas flow that is employed duringthe gas pulsing on phase.

The gas pulsing rate is limited at the high end (upper frequency limit)by the residence time of the gas in the chamber. This residence timeconcept is one that is known to one skilled in the art and varies fromchamber design to chamber design. For example, residence time typicallyranges in the tens of milliseconds for a capacitively coupled chamber.In another example, residence time typically ranges in the tens ofmilliseconds to hundreds of milliseconds for an inductively coupledchamber.

In one or more embodiments, the gas pulsing period may range from 10milliseconds to 50 seconds, more preferably from 50 milliseconds toabout 10 seconds and preferably from about 500 milliseconds to about 5seconds.

The source RF pulsing period is lower than the gas pulsing period inaccordance with embodiments of the invention. The RF pulsing frequencyis limited at the upper end by the frequency of the RF signal (e.g.,13.56 MHz would establish the upper limit for the RF pulsing frequencyif the RF frequency is 13.56 MHz).

FIG. 4 shows, in accordance with one or more embodiments of theinvention, other possible combinations. In FIG. 4, another signal 406(such as bias RF or any other periodic parameter) may be pulsed alongwith gas pulsing signal 402 and source RF pulsing signal 404 (pulsed asshown with 430 and 432). The pulsing of signal 406 may be madesynchronous or asynchronous with any other signals in the system.

Alternatively or additionally, another signal 408 (such as DC bias ortemperature or pressure or any other non-periodic parameter) may bepulsed along with gas pulsing signal 402 and source RF pulsing signal404. The pulsing of signal 408 may be made synchronous or asynchronouswith any other signals in the system.

Alternatively or additionally, another signal 410 (such as RF source orRF bias or any other non-periodic parameter) may be chirped and pulsedalong with gas pulsing signal 402. For example, while signal 410 ispulsing, the frequency of signal 410 may vary depending on the phase ofsignal 410 or another signal (such as the gas pulsing signal) or inresponse to a control signal from the tool control computer. In theexample of FIG. 1, reference 422 points to a region of higher frequencythan the frequency associated with reference number 420. An example of alower frequency 422 may be 27 MHz and a higher frequency 420 may be 60MHz. The pulsing and/or chirping of signal 410 may be made synchronousor asynchronous with any other signals in the system.

FIG. 5 shows, in accordance with an embodiment of the invention, thesteps for performing combination pulsing. The steps of FIG. 5 may beexecuted via software under control of one or more computers, forexample. The software may be stored in a computer readable medium,including a non-transitory computer readable medium in one or moreembodiments.

In step 502, a substrate is provided in a plasma processing chamber. Instep 504, the substrate is processed while pulsing both the RF sourceand the input gas. Optional pulsing of one or more other signals (suchas RF bias or another signal) is shown in step 506. In step 508, thefrequency, duty cycle, gas percentages, etc. may optionally be variedwhile pulsing the RF source and the input gas.

In one or more embodiments, the gas is pulsed such that there are atleast two phases per cycle, with cycles repeating periodically. Theother parameters, including the RF source signal, may be left unpulsed.During the first phase, the reactant gas (which may comprise multipledifferent etching and/or polymer-forming gases) to inert gas (such asone or more of Argon, Helium, Xenon, Krypton, Neon, etc.) ratio is at afirst ratio. During the second phase, the reactant gas to inert gasratio is at a second ratio different from the first ratio. If the ratioof reactant gas flow to total gas flow into the chamber is reduced(i.e., the ratio of inert gas to total gas flow into the chamber isincreased) during the second phase, the chamber contains a higherpercentage of the inert gas during the second phase than in the firstphase. In this case, an ion-dominant plasma results wherein the plasmaion flux is formed primarily with inert gas to perform the etching.

This is unlike the prior art situation where reactant gas is added topulse the gas. By increasing the percentage of the inert gas in thechamber without increasing the reactant gas flow into the chamber,embodiments of the invention achieve an ion-rich plasma to improve etchuniformity, directionality and/or selectivity.

In an embodiment, the ratio is changed not by adding any reactant (suchas etchant or polymer-forming) gases into the chamber but by reducingthe reactant gases flow rate such that the flow percentage of inert gasto reactant gas increases. In this embodiment, the chamber pressurewould inherently reduce during the second phase.

Alternatively or additionally, the ratio of reactant gas(es) to inertgas(es) may be changed by increasing the inert gas(es) flow into thechamber while keeping the reactant gas(es) flow into the chamber eitherconstant or by reducing the reactant gas(es) flow (but not by increasingthe reactant gases flow into the chamber). In an embodiment, the flow ofinert gas is increased to offset the reduction in the flow of reactantgas. In this embodiment, the chamber pressure remains substantially thesame during the first and second phases. In another embodiment, the flowof inert gas is increased but is insufficient to fully offset thereduction in the flow of reactant gas. In this embodiment, the chamberpressure is reduced during the second phase. In another embodiment, theflow of inert gas is increased more than sufficient to offset thereduction in the flow of reactant gas. In this embodiment, the chamberpressure is increased during the second phase.

As mentioned, in one or more embodiments, during the gas pulsing secondphase, the percentage of inert gas(es) to total gas(es) flowed into thechamber may vary from about X% to about 100%, wherein X is thepercentage of inert gas(es) to total gas flow that is present when theplasma chamber is stabilized for processing or the percentage of inertgas(es) to total gas flow that is present during the first phase. In amore preferred embodiment, the percentage of inert gas(es) to totalgas(es) flowed into the chamber may vary from about 1.1 X to about 100%.In a preferred embodiment, the percentage of inert gas(es) to totalgas(es) flowed into the chamber may vary from about 1.5 X to about 100%during the second phase.

The gas pulsing rate is limited at the high end (upper frequency limit)by the residence time of the gas in the chamber. As mentioned, forexample, residence time typically ranges in the tens of milliseconds fora capacitively coupled chamber. In another example, residence timetypically ranges in the tens of milliseconds to hundreds of millisecondsfor an inductively coupled chamber. Also as mentioned, in one or moreembodiments, the gas pulsing period may range from 10 milliseconds to 50seconds, more preferably from 50 milliseconds to about 10 seconds andpreferably from about 500 milliseconds to about 5 seconds.

In one or more embodiments, the inert gas added during the second phaseof the periodic pulsing may be the same inert gas or a different inertgas with different chemical composition and/or different constituentgases. Alternatively or additionally, the duty cycle of the gas pulsingrate may vary from 1% to 99%. Alternatively or additionally, the gaspulsing rate may be chirped, i.e., may change, during processing. Forexample, the gas pulsing may be done with a 5-second gas pulsing periodwith a 40% duty cycle and then switched to a 9-second gas pulsing periodwith either the same 40% duty cycle or a different duty cycle. Thechirping may be done periodically in accordance with a chirpingfrequency (such as 20 second chirping frequency wherein the gas pulsingfrequency may be changed every 20 seconds).

FIG. 6 shows, in accordance with one or more embodiments of theinvention, the steps for performing gas pulsing. The steps of FIG. 6 maybe executed via software under control of one or more computers, forexample. The software may be stored in a computer readable medium,including a non-transitory computer readable medium in one or moreembodiments.

In step 602, a substrate is provided in a plasma processing chamber. Instep 604, a plasma is generated in the chamber and stabilized with abaseline ratio of inert gas flow to reactant gas flow. In step 606, theratio of inert gas flow to reactant gas flow is increased in one phaseof the gas pulsing without increasing the reactant gas flow into thechamber. In step 608, the ratio of inert gas flow to reactant gas flowis decreased, relative to the ratio of inert gas flow to reactant gasflow of step 606, in another phase of the gas pulsing without increasingthe reactant gas flow into the chamber. In various embodiments, theratio of inert gas flow to reactant gas flow in step 608 may be thesubstantially the same as the ratio of inert gas flow to reactant gasflow of step 604 (stabilize plasma step) or may be higher or lower thanthe ratio of inert gas flow to reactant gas flow of stabilize step 604.In step 610, the substrate is processed while the gas is pulsed byhaving the aforementioned inert-to-reactant flow ratio fluctuatesperiodically with the ratios of steps 606 and 608.

FIGS. 7A and 78 illustrate, in accordance with embodiments of theinvention, different example variations of the gas pulsing schemediscussed in connection with FIG. 6. In the example of FIG. 7A, cases A,C, D, and E represents the various ratio of inert gas to reactant gas.In case A, the ratio of inert gas (I) to reactant gas (R) is 3:7, forexample. In case B, the ratio of inert gas to reactant gas is 8:1, forexample. In case C, the ratio of inert gas to reactant gas is 1:9, forexample. In case D, the gas flow into the chamber is essentially allinert. While example ratio values are given, the exact values of theratios are only illustrative; the important point is that these casesall have different ratios relative to one another.

In FIG. 7B, an example pulsing 702 may be ADAD in a preferred embodimentwhere the gas pulse may fluctuate periodically between case A and case Dof FIG. 7A and repeat.

Another example pulsing 704 may be ABABAB/ADAD/ABABAB/ADAD where the gaspulse may fluctuate periodically between case A and case B of FIG. 7A,then between cases A and D of FIG. 7A, and then back to cases A and B ofFIG. 7A and repeat.

Another example pulsing 706 may be ABABAB/ACAC/ABABAB/ACAC where the gaspulse may fluctuate periodically between case A and case B of FIG. 7A,then between cases A and D of FIG. 7A, and then back to cases A and B ofFIG. 7A and repeat.

Another example pulsing 708 may be ABABAB/CDCD/ABABAB/CDCD where the gaspulse may fluctuate periodically between case A and case B of FIG. 7A,then between cases C and D of FIG. 7A, and then back to cases A and B ofFIG. 7A and repeat.

Another example pulsing 710 may be ABABAB/CDCD/ADAD/ABABAB/CDCD/ADADwhere the gas pulse may fluctuate periodically between case A and case Bof FIG. 7A, then between cases C and D of FIG. 7A, then between cases Aand D of FIG. 7A and then back to cases A and B of FIG. 7A and repeat.

Other examples may include 4 phases such as ABAB/CDCD/ADAD/ACAC andrepeat. The complex pulsing is highly advantageous for processesinvolving, for example, in-situ etch-then-clean or multi-step etches,etc.

In another embodiment, the gas pulsing of FIGS. 6, 7A and 7B may becombined with asynchronous or synchronous pulsing of the RF bias signalthat is supplied to the powered electrode. In an example, when the gasis pulsed to a high inert gas percentage or 100% or near 100% inert gaspercentage in one phase of the gas pulsing cycle, the RF bias signal ispulsed high. When the gas is pulsed to a lower inert gas percentage inanother phase of the gas pulsing cycle, the RF bias signal is pulsed lowor zero. In various embodiments, the pulsing frequency of the RF biassignal may be the same or different compared to the pulsing frequency ofthe gas pulsing. In various embodiments, the duty cycle of the RF biassignal may be the same or different compared to the duty cycle of thegas pulsing. Chirping may be employed with one or both of the RF biassignal pulsing and the gas pulsing if desired.

In each of the gas pulsing examples, the pulsing frequency, the numberof pulses, the duty cycle, etc., may be varied kept constant throughoutthe etch or may vary periodically or non-periodically as required.

As can be appreciated from the foregoing, embodiments of the inventionprovide another control knob that can widen the process window for etchprocesses. Since many current plasma chambers are already provided withpulsing valves or pulsing mass flow controllers, the implementation ofgas-pulsing in accordance with FIGS. 6-7A/7B and the discussion hereinmay be achieved without requiring expensive hardware retrofitting.Further, if RF pulsing is desired in conjunction with gas pulsing, manycurrent plasma chambers are already provided with pulse-capable RF powersupplies. Accordingly, the achievement of a wider process window viagas/RF power pulsing may be obtained without requiring expensivehardware retrofitting. Current tool owners may leverage on existing etchprocessing systems to achieve improved etches with minor softwareupgrade and/or minor hardware changes. Further, by having improvedand/or more granular control of the ion-to-radical flux ratios,selectivity and uniformity and reverse RIE lag effects may be improved.For example, by increasing the ion flux relative to radical flux mayimprove the selectivity of one layer to another layer on the substratein some cases. With such improved control of ion-to-radical, atomiclayer etch (ALE) may be more efficiently achieved.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents, whichfall within the scope of this invention. For example, the pulsingtechniques discussed in the figures may be combined in any combinationto suit the requirement of a particular process. For example, the dutycycle variance may be practiced with techniques discussed with any one(or part of any one or a combination of multiple ones) of the figures.Likewise, the frequency chirping may be practiced with techniquesdiscussed with any one (or part of any one or a combination of multipleones) of the figures and/or with duty cycle variance. Likewise, inertgas substitution may be practiced with techniques discussed with any one(or part of any one or a combination of multiple ones) of the figuresand/or with duty cycle variance and/or with frequency chirping. Thepoint is although techniques are discussed individually and/or inconnection with a specific figure, the various techniques can becombined in any combination in order to perform a particular process.

Although various examples are provided herein, it is intended that theseexamples be illustrative and not limiting with respect to the invention.Also, the title and summary are provided herein for convenience andshould not be used to construe the scope of the claims herein. If theterm “set” is employed herein, such term is intended to have itscommonly understood mathematical meaning to cover zero, one, or morethan one member. It should also be noted that there are many alternativeways of implementing the methods and apparatuses of the presentinvention.

What is claimed is:
 1. A method for processing a substrate in a plasmaprocessing chamber of a plasma processing system, said plasma processingchamber having at least one plasma generating source and at least a gassource for providing a process gas into an interior region of saidplasma processing chamber, comprising: exciting said plasma generatingsource with an RF signal having an RF frequency; and pulsing said gassource, using at least a first gas pulsing frequency, such that a firstprocess gas is flowed into said plasma processing chamber during a firstportion of a gas pulsing period associated with said first gas pulsingfrequency and a second process gas is flowed into said plasma processingchamber during a second portion of said gas pulsing period associatedwith said first gas pulsing frequency, said second process gas having alower reactant-gas-to-inert-gas ratio relative to areactant-gas-to-inert-gas ratio of said first process gas, wherein saidsecond process gas is formed by removing at least a portion of areactant gas flow from said first process gas.
 2. The method of claim 1wherein said plasma processing chamber represents an inductively coupledplasma processing chamber and said at least one plasma generating sourcerepresents at least one inductive antenna.
 3. The method of claim 1wherein said plasma processing chamber represents capacitively coupledplasma processing chamber and said at least one plasma generating sourcerepresents an electrode.
 4. The method of claim 1 wherein said pulsingsaid gas source further comprising flowing a higher flow of an inert gasduring said second portion of said gas pulsing period relative to a flowof said inert gas during said second portion of said gas pulsing periodto at least partially compensate for a pressure drop caused by saidremoving said at least a portion of said reactant gas flow.
 5. Themethod of claim 1 wherein said pulsing said gas source furthercomprising flowing a higher flow of an inert gas during said secondportion of said gas pulsing period relative to a flow of said inert gasduring said second portion of said gas pulsing period to fullycompensate for a pressure drop caused by said removing said at least aportion of said reactant gas flow.
 6. The method of claim 1 wherein saidpulsing said gas source further comprising flowing a higher flow of aninert gas during said second portion of said gas pulsing period relativeto a flow of said inert gas during said second portion of said gaspulsing period to more than fully compensate for a pressure drop causedby said removing said at least a portion of said reactant gas flow. 7.The method of claim 1 wherein said pulsing said gas source furthercomprising flowing a third process gas into said plasma processingchamber during a third portion of said gas pulsing period associatedwith said gas pulsing period, wherein said third process gas has areactant-gas-to-inert-gas ratio that is different from areactant-gas-to-inert-gas ratio associated with said first process gas,said third process gas has said reactant-gas-to-inert-gas ratio that isalso different from a reactant-gas-to-inert-gas ratio associated withsaid second process gas.
 8. The method of claim 7 wherein said pulsingsaid gas source further comprising flowing a fourth process gas intosaid plasma processing chamber during a fourth portion of said gaspulsing period associated with said gas pulsing period, wherein saidfourth process gas has a reactant-gas-to-inert-gas ratio that isdifferent from said reactant-gas-to-inert-gas ratio associated with saidfirst process gas, said fourth process gas has saidreactant-gas-to-inert-gas ratio that is also different from saidreactant-gas-to-inert-gas ratio associated with said second process gas,said fourth process gas has said reactant-gas-to-inert-gas ratio that isalso different from said reactant-gas-to-inert-gas ratio associated withsaid third process gas.
 9. The method of claim 7 wherein said pulsingsaid gas source further includes pulsing said second gas source using asecond gas pulsing frequency, wherein gas pulsing during a pulsingperiod associated with said second gas pulsing frequency is differentfrom gas pulsing period associated with said first gas pulsingfrequency.
 10. The method of claim 1 wherein said gas pulsing periodassociated with said first gas pulsing frequency is between about 10milliseconds and about 50 seconds.
 11. The method of claim 1 whereinsaid gas pulsing period associated with said first gas pulsing frequencyis between about 50 milliseconds and about 10 seconds.
 12. The method ofclaim 1 wherein said gas pulsing period associated with said first gaspulsing frequency is between about 500 milliseconds and about 5 seconds.13. The method of claim 1 wherein a percentage of inert gas in saidfirst process gas is about 1.1X to about 100%, wherein X represents apercentage of inert gas in said second process gas.
 14. The method ofclaim 1 wherein a percentage of inert gas in said first process gas isabout 1.5X to about 100%, wherein X represents a percentage of inert gasin said second process gas.
 15. The method of claim 1 wherein saidpulsing said gas source further comprising providing a flow of an inertgas during said second portion of said gas pulsing period, said inertgas is different from inert gas present in said first process gas. 16.The method of claim 1 wherein said pulsing said gas source employs aconstant duty cycle.
 17. The method of claim 1 wherein said pulsing saidgas source employs a varying duty cycle.
 18. The method of claim 1wherein said pulsing said gas source employs frequency chirping.
 19. Themethod of claim 1 further comprising pulsing an RF signal that isprovided to an RF source of said plasma processing chamber, said pulsingsaid RF signal is performed during said pulsing said gas source, saidpulsing said RF signal uses an RF signal pulsing frequency that isdifferent from said first gas pulsing frequency.
 20. The method of claim19 further comprising pulsing another parameter other than said RFsignal and said gas source, using another pulsing frequency that isdifferent from said RF signal pulsing frequency and said first gaspulsing frequency, during said pulsing said RF signal and said pulsingsaid gas source.
 21. A method for processing a substrate in a plasmaprocessing chamber of a plasma processing system, said plasma processingchamber having at least one plasma generating source and at least a gassource for providing a process gas into an interior region of saidplasma processing chamber, comprising: a) exciting said plasmagenerating source with an RF signal having an RF frequency; b)processing said substrate by forming a first plasma with a first processgas, said first process gas having a first reactant-gas-to-inert-gasratio; and c) processing said substrate by forming a second plasma witha second process gas, said second process gas having a secondreactant-gas-to-inert-gas ratio, wherein said secondreactant-gas-to-inert-gas ratio is achieved without adding reactant gasto said first process gas and wherein said firstreactant-gas-to-inert-gas ratio is achieved without adding reactant gasto said second process gas.
 22. The method of claim 21 wherein saidsecond reactant-gas-to-inert-gas ratio is achieved by adding inert gasflow to said first process gas.